Caenorhabditis elegans MAI-1 protein, which is similar to mitochondrial ATPase inhibitor (IF1), can inhibit yeast F0F1-ATPase but cannot be transported to yeast mitochondria.

In Caenorhabditis elegans, two proteins that are similar to mitochondrial ATPase inhibitor protein (IF(1)) have been found and named MAI-1 and MAI-2. In this study, we overexpressed and purified both the proteins and examined their properties. Circular dichroism spectra indicated that both the MAI-1 and MAI-2 predominantly consisted of beta- and random structure, and in contrast to mammalian IF(1), alpha-helixes were barely detected. Both MAI-1 and MAI-2 could inhibit yeast F(0)F(1)-ATPase, but the inhibition by MAI-1 was pH-independent. MAI-2-GFP fusion protein was transported to yeast mitochondria, but MAI-1-GFP was not. These results indicate that the MAI-2 is (C. elegans) IF(1). MAI-1 seems to be a cytosolic protein and may regulate cytosolic ATPase(s).